1. Field of the Invention
The present invention relates to a wireless communication apparatus and an operating frequency control method of a power conversion apparatus.
Priority is claimed on Japanese Patent Application No. 2005-246609, filed Aug. 26, 2005, the content of which is incorporated herein by reference.
2. Description of the Related Art
In recent years, a communication module including a wireless communication function (wireless communication apparatus) is set into or built in various apparatuses and a communication system which obtains information via the communication module and operates remote monitoring or information management of the apparatuses is attracting public attention (for example, managing stored goods information or change information of a vending machine, remote monitoring of the operating state of industrial equipment and the like).
Some of the communication modules described above receive power supply from an external power source and operate. Such communication modules include a DC/DC converter (power conversion apparatus) and power supply voltage is supplied to each element of the communication module after converting the voltage by the DC/DC converter. In this operation, due to an operating frequency of the DC/DC converter, conduction noise on a power line between the external power source and the DC/DC converter occurs. Therefore, in case where the external power source supplies the power not only to the communication module but also to other electric apparatuses, or where the power line from the external power source is designed to be set close to the other electric apparatuses, if the operating frequency of the DC/DC converter coincides with a frequency band which has harmful effects on the other electric apparatuses, then there is possibility such that the conduction noise occurring on the power line has a negative influence on the other electric apparatuses. Hence, provision of an additional circuit such as a filter is required in order to prevent the conduction noise on the communication module.
For example, in Japanese Patent Application, First Publication No. 2002-51005, a structure of a relay apparatus which relays TV broadcasting (including cable TV) and is able to operate wireless communication in the case of emergency is disclosed. Such structure in which the transmitter-receiver operating wireless communication has lines closely set to apparatuses operating other broadcasting or the like is generally increasing. In such apparatuses, not only considerations with respect to the wireless communication as described above, but also considerations with respect to means which operate broadcasting or the like are needed. Naturally, other than receiving broadcasting, when an apparatus which is easily affected by a certain frequency band because of operating very accurate measuring or the like is set closely, it is necessary for the wireless communication apparatus to prevent emitting at least in the certain frequency band. Even though emission from the wireless communication apparatus itself can be prevented by the shielding case or the like, consideration of other solutions is needed with respect to radiation noise from the power line.
However, when the filter is provided at the communication module as described above, there is a problem in which the cost of the communication module increases and the size of a circuit board is increased (that is, the communication module becomes larger). In recent years, there has been a strong need for a smaller communication module and for decreasing cost, therefore, in view of such points, it is a big problem to decrease a negative influence on the other electric apparatuses because of the conduction noise along with preventing increasing cost and an increase in size of communication module.